Multiple species implants with pulsed and DC plasma immersion ion implantation

Plasma Immersion Ion Implantation (PIII) is an emerging implant technology for high dose and low energy applications. Since PIII does not contain mass separation, all ion species in the plasma are implanted into the wafer. By utilizing an effective mass and an effective Bohm velocity for the plasma, the single species PIII model has been extended to multiple species. This model includes two components of ion current, the ions uncovered by the expanding sheath, and ions that diffuse across the sheath boundary. This new model calculates the dose rates for all the ion species in the plasma, and is valid for pulsed and DC PIII. Calculation and simulation show that the percentage of each ion implanted is a function of the pulse width. For a plasma containing 10% He/sup +/ and 90% PH/sub 3//sup +/, the implant is 90% PH/sub 3//sup +/ for short pulses, and only 76% PH/sub 3//sup +/ for longer pulses. For proper calibration and dosimetry it is imperative to understand that changing the pulse width will alter the implant ratios.